Method for assembling ceramic plug to lead wires for electric blasting caps



23153112 METHOD FOR'ASSEMBLING CERAMIC PLUG TO LEAD WIRES FOR ELECTRIC BLASTING'CAAPS Mathew ,Carl Hengel, Latrobe, Pa., assignpr to American Cyanamd Company, New York, N`.Y.,` a corporation of Maine .e

,Application August s, '1956, 'Serial No. 2,855

. 2 Claims. Cl. o2-zs This invention relates'to the production of an electric blasting initiatorand more particularly to a method of sealing the lead' wires into the ignition plugin an electric blasting cap and to a new article comprising an ignition plug with lead wires aflixed therein by` expansion against the walls of the wire holes in the plug.

In the past, electric blasting intiators have been assembled with insulated lead wires positioned and Secured by a plugor bnshing' of sulfur, rubber or plastic composition' The' wires that pass through the plug are attachedjthereto by physical or Chemical adheson since the plug had been' formedor molded about a section near one end of the wires. Frequently, the wire encompassed by the plug is formed into a symmetrically tortuous pattern, to improve the tensle strength of the bond between the wires and the plug' The plug is positioned in and retained within the open end of the metal capsule or shell by a sealwhich is 'formed in place by alternate layersof moltensulfur and asphaft by 'thermoplastic compositionsor in .the case 'of rubber plugs, .by crim'ping the'walls of thecapsule into .the body of the plug. These prior methodsof assembly in constructon result in a product with'a limited resistance to deformation, temperature variations,-and ngress of water.

'It' has beenproposed to replace such a molded` plugwith a -preforrned ceramic plug. In the co-pending application of G. Bayard Young, Serial No. 449,175, filed August 11, 1954, now Patent Number 2,882,820, the preparation of such a ceramic plug is described. Ceramic plugs have the advantage of unusual resistance to extremes of pressure, temperature, and physical abuse as well as unusual resistance to water penetration. However, the sealing of the lead wires into a ceramic plug presents a very ditlicult problem' In the past, the lead wires have been fixed in ceramic pieces by one of two methods. In one, the cerarnic is metallized around the holes through which the lead wires are inserted and the lead wires are then soldered to the metallized coating. Alternatively, the ceramic is silvered and then fired to produce a metal coating to which the lead wires may be soldered. In soldering small joints, it is difiicult to avoid the formation of a brittle union because of cold soldering and the danger of this presents a still further disadvantage of the previous method.

According to the present invention, I have found a greatly simplified method of sealing the leadwires in a plug so that they will not shift when stress or strain is placed upon them. My method comprses swaging the wire into a recess in the spaced holes for the insertion of the wire while passing an electrc current through the wire in such a manner as to soften the wire at the proper point.

It is an advantage of my invention that there are eliminated the difficult steps involvedin obtaining a seal between the wire and the plug. There is no need to silver or otherwise metallize the interior of the bore through the plug and the elimination of such a step is an obvous economy measure. It is a further advantage of '2 the process of my invention that the need 'for use of solder on' the plug is eliminated; Both the steps of metallizing or silvering and the step of soldering are tedious and to be done properly must bevdone by hand. In my invention these steps are eliminated and the sealing of the wire into the plug can be carried out simply and automatically.

In carrying out the process of my invention, there is used a plug which has been cast with a recess in the' holes for the insertion of the wires. The plug may be composed of any suitable rigid material such as porcelain, glass or a thermo-setting resin such as the phenol formaldehyde type. However, because of their rigidity, high dielectric properties, and low cost, ceramic plugs are preferred. The holes for the lead wires are formed in such a plug during' thecasting and firing of the plug, but in those of a resinous material, they can be drilled out after the plug has been formed or` can be formed by the extension die. 'They are spaced exactly the right distance apart for the lead wires. In each hole there g is preferably a recess into which the wire is to be swaged.

This recess may be anywhere in the hole, but preferably, because of ease of manufacture, it is in the form of a counterbored hole of somewhat larger diameter at one end of the lead holes The holes must be spaced exactly in the plug in order to keep the bridge wire length always the same, since such length governs the amount of current needed to 'explode the initiating charge in the cap.

The process of my invention ,will be more clearly understood with reference to the accompanying drawing.

Figure 1 is a sectionl side view of an electric blasting cap plug through which the wires have been inserted and to which one` pair ofelectrodes has, been fastened, in preparaton for the swaging operation;

Figure `2 is :a sectional sideview of the same electric i blastingcap plug after the.wires have been swaged into place;

Figure 3 is a sectional side view of an electric blasting cap plug'of a different modification in which' the recess is in the 'middle of the bore and ,the wires have been swaged. into the saidrecess;

Figure 4 is a sectional'side view of an electric blasting' caphaving no recess for the exp-ansion .of the wire, and

Figure 5 is an end view of the plug of Figure 1 on the end 5-5, without the wire in place.

In Figure 1 an electric blasting cap plug 1 has been provided with two carefully spaced holes 2. At one end of each bore is a larger counterbored recess in the bored hole 3. The lead wires 4 have been inserted in the holes through the plug. To one of the wires has been clamped a pair of electrodes 5 and 6. Electrode 5 is stationary and electrode 6 is movable, but by being clamped to the wire it remains stationary, holding spring 7 compressed. The spacing of the electrodes is such that the midway point between them occurs in the middle of the recess in the bore 3. Normally two pairs of electrodes are used so that both wires are swaged simultaneously. Alternatively, each wire can be swaged individually and for Simplicity Figure 1 shows this modification.

In Figure 2 the same electric blasting cap plug and lead wires are shown after the wires have been swaged into place. The wire has expanded, forming an enlarged portion 8, into the recesses 3 in such a way as to lock the wire in place. The looking is done not only by the fact that the expansion prevents the wire from sliding through the narrower diameter bore, but also because'the bulged portion 8 has been pushed tghtly against the contour of the recess 3.

In Figure 3 an electric blasting cap plug is shown with wires in place, completely swaged. This, however, is a modification in which the recess 9 is not at one end of the wire holes but in the middle, making a more perfect Patented Dec. 1, 1959 p brdge wire;

when the lead'wires are pulledgard therecesshis preferablyplaced at' the end of` the' plug -whi'ch is" jnearestthe u r However,` it can he placed anywhere in the I hole depending on the ease with which such "a recess can he s constructed.- `Sucha recess Can be constructe'd by y u drilling` with 'expandible drill or other tooLknown 'to the adequate looking can be obtained there.`

i i In practice, it is'not necessary tohave arecess, although` suchis the preferred modifieationi'ofny invention. r In its ?btoadest sense myrirventi'on includes theprocess of i swaging; or expanding the leadwires againstthe Walls of r z r v the wire holes in' a' plugin' which the 'said holes have'no recess: This :is: illustrated in Figre An effective lock r ing canbe obtainedbythis modification because theiv v `'10 art or'by casting withacollapsible mandreL* Thismodi'- fietion is more expensive to manufacture and that of Fiure `1 'and FigureZis for this ,reason preferablesince i side of the ,wire'hole '2 will not' be' completely smooth i tightly' 'against the walls, cannot slide in either-direction.

r However, 'a 'recess is greatlyto be preferred', since it does u i not depend on uncontrollablei'irregularities `'for `'the efiir z 'In practiee it has been' 'foimd advant ageous; although not'necessary to have *the recess 'made'with a attened surface. This permts the' swagng to prevent therotation v of the wire in theholes' zas well ;as'sliding out of the r and 'the wire will be pushed' atthe expanded point 8'in`to i the irregularitiesin the wall.-` The wirebeng' exparded r 7 holes. In Figure 5, such a modification is shown; The

` flat surface-110 looks.` the wiresmorefirmly after-'being z swaged into therecjessfi :and prevents rotation within the i hole 2.

The electrodes which furnishthe'electriccurreit' for` v 'thei swagngcan he of standard type clamping rigidlyyon r r the lead wire. The clamping'mustgbe rigid -becausethe electnodes are alsoused, prefe'ably,` to furnishthe 'com-` pression `necessary to expard the.softened metal of' the wire's. At least one ofthe electrodes `is movableand metal. ,Alternatively, separate rigid clamps can `beprovided to supply, thepressure, necessary to expand, the u softened wire, in which casethe electrodes can `'be simple' r electrical connection of anytemporary typewhich clamps one' wire 'on' another., r r I The postoning of the electrodes on the wire is imr portant since the softening will occur halfway between them.` The positioning' must theretorebecalculated to 7 `put the halfwajw'point: at the ispot Where theeXpansion is desired.

-' When a 22` gaugecopperwire is`us`e'd as; the lead, wire,"

z &potential of 'voltsand a current of '10 amperes 'is supplied to the system, Wires of `'greater thicknessorother metals take greater current; i In general, ia i low r :current is suppledwandmis gradually increased until the Wire, is softened ?and swaging occurs; `'Normally, this 'occurs quite rapidly and only a brief passage of the elec trodecurrent is needed to effect swaging; i r r r r -I,c1aim:` r r 1.' An electtie'blastingcap plug assembly which com'- pris'es a ce-amicelectric blasting cap plug, two apertures I `ftf' leat wires 'extendng longitudinally through said, i plug; 'each 'of said ape ftureshaving an enlarged portion substantially midwayof its length, lead wires in `eaehof I r r saidaperturesysaid lead Wires'having anexpanded idiameter'within said' ehlarged portion of the apertures completely filling said enlarged portion, saidrlead wires being: r 2

rigidlyaflixed in said plug by saidexpandeddiameters.

portionhas a. flattened surface." i u I NITED TA ES PATENTS i 2,` 240,4 3s 2,377,804 J 'Na'varte June '5, 1945 58 8 Stuart O ct,31, 1950 i i 2,7393691 r Cooney `Mar.27, 1956 2,776,`467.- Brennan Jan.' 8, 1957 i r FOREIGNPATENTS t t r 6,079 Great Britain 1908` 434,842 Great Brtan Sept. 10, 1935 Great Britain" Feb. 27, 1942 i 

